package com.koushikdutta.ion.gif;

import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.util.Log;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.Arrays;

public class GifDecoder implements Cloneable {

	public static final int STATUS_PARSING = 0;
	public static final int STATUS_FORMAT_ERROR = 1;
	public static final int STATUS_OPEN_ERROR = 2;
	public static final int STATUS_FINISH = -1;
	
	private int status;

	public int width; // full image width
	public int height; // full image height
	private boolean gctFlag; // global color table used
	private int gctSize; // size of global color table
	private int loopCount = 1; // iterations; 0 = repeat forever

	private int[] gct; // global color table
	private int[] lct; // local color table
	private int[] act; // active color table

	private int bgIndex; // background color index
	private int bgColor; // background color
	private int lastBgColor; // previous bg color
	private int pixelAspect; // pixel aspect ratio

	private boolean lctFlag; // local color table flag
	private boolean interlace; // interlace flag
	private int lctSize; // local color table size

	private int ix, iy, iw, ih; // current image rectangle
	private int lrx, lry, lrw, lrh;


	private byte[] block = new byte[256]; // current data block
	private int blockSize = 0; // block size
	private int dispose = 0;
	private int lastDispose = 0;
	private boolean transparency = false; // use transparent color
	private int delay = 0; // delay in milliseconds
	private int transIndex; // transparent color index

	private static final int MaxStackSize = 4096;
	// max decoder pixel stack size

	// LZW decoder working arrays
	private short[] prefix;
	private byte[] suffix;
	private byte[] pixelStack;
	private byte[] pixels;

	private byte[] gifData = null;
	private int gifDataOffset;
	private int gifDataLength;

    private int readBytes;
    private int currentFrame;

    GifFrame lastFrame;
    GifFrame restoreFrame;
    int[] dest;

    public GifDecoder mutate() {
        try {
            GifDecoder ret = (GifDecoder)clone();
            block = new byte[256];
            prefix = null;
            suffix = null;
            pixelStack = null;
            pixels = null;
            dest = null;
            return ret;
        }
        catch (CloneNotSupportedException e) {
            throw new AssertionError(e);
        }
    }

    public ByteBuffer getByteBuffer() {
        return ByteBuffer.wrap(gifData, gifDataOffset, gifDataLength);
    }

    public int getWidth() {
        return width;
    }

    public int getHeight() {
        return height;
    }

    public int getGifDataLength() {
        return gifDataLength;
    }

    public GifFrame getLastFrame() {
        return lastFrame;
    }

    public GifDecoder(ByteBuffer bb) {
        this(bb.array(), bb.arrayOffset() + bb.position(), bb.remaining());
    }

    public GifDecoder(byte[] data){
		this(data, 0, data.length);
	}

	public GifDecoder(byte[] data,int offset,int length) {
        gifData = data;
        gifDataOffset = offset;
        gifDataLength = length;

        restart();
    }

    public void restart() {
        readBytes = 0;
        status = STATUS_PARSING;
        gct = null;
        lct = null;
        readHeader();
    }

    public synchronized GifFrame nextFrame() {
        // read GIF file content blocks
        while (!err() && status == STATUS_PARSING) {
            int code = read();
            switch (code) {
                case 0x2C: // image separator
                    return lastFrame = readImage();
                case 0x21: // extension
                    code = read();
                    switch (code) {
                        case 0xf9: // graphics control extension
                            readGraphicControlExt();
                            break;
                        case 0xff: // application extension
                            readBlock();
                            String app = "";
                            for (int i = 0; i < 11; i++) {
                                app += (char) block[i];
                            }
                            if (app.equals("NETSCAPE2.0")) {
                                readNetscapeExt();
                            } else {
                                skip(); // don't care
                            }
                            break;
                        default: // uninteresting extension
                            skip();
                    }
                    break;
                case 0x3b: // terminator
                    status = STATUS_FINISH;
                    return null;
                case 0x00: // bad byte, but keep going and see what happens
                    break;
                default:
                    status = STATUS_FORMAT_ERROR;
            }
        }

        status = STATUS_FORMAT_ERROR;
        return null;
    }

	public int getStatus(){
		return status;
	}
	
	public boolean parseOk(){
		return status == STATUS_FINISH;
	}

	public int getLoopCount() {
		return loopCount;
	}

	private Bitmap setPixels() {
        if (lastDispose == 2) {
            if (dest == null)
                dest = new int[width * height];
            int c = 0;
            if (!transparency) {
                c = lastBgColor;
            }
            Arrays.fill(dest, c);
        }
        else {
            if (dest == null) {
                dest = new int[width * height];
                if (restoreFrame != null)
                    restoreFrame.image.getPixels(dest, 0, width, 0, 0, width, height);
                else
                    Arrays.fill(dest, 0);
            }
            else if (lastDispose == 3) {
                // force restore on dispose method restore previous
                if (restoreFrame != null)
                    restoreFrame.image.getPixels(dest, 0, width, 0, 0, width, height);
                else
                    Arrays.fill(dest, 0);
            }
        }

        // copy each source line to the appropriate place in the destination
		int pass = 1;
		int inc = 8;
		int iline = 0;
		for (int i = 0; i < ih; i++) {
			int line = i;
			if (interlace) {
				if (iline >= ih) {
					pass++;
					switch (pass) {
					case 2:
						iline = 4;
						break;
					case 3:
						iline = 2;
						inc = 4;
						break;
					case 4:
						iline = 1;
						inc = 2;
					}
				}
				line = iline;
				iline += inc;
			}
			line += iy;
			if (line < height) {
				int k = line * width;
				int dx = k + ix; // start of line in dest
				int dlim = dx + iw; // end of dest line
				if ((k + width) < dlim) {
					dlim = k + width; // past dest edge
				}
				int sx = i * iw; // start of line in source
				while (dx < dlim) {
					// map color and insert in destination
					int index = ((int) pixels[sx++]) & 0xff;
                    if (!transparency || index != transIndex) {
                        dest[dx] = act[index];
					}
					dx++;
				}
			}
		}
		return Bitmap.createBitmap(dest, width, height, Config.ARGB_4444);
	}

	private void decodeImageData() {
		int NullCode = -1;
		int npix = iw * ih;
		int available, clear, code_mask, code_size, end_of_information, in_code, old_code, bits, code, count, i, datum, data_size, first, top, bi, pi;

		if ((pixels == null) || (pixels.length < npix)) {
			pixels = new byte[npix]; // allocate new pixel array
		}
		if (prefix == null) {
			prefix = new short[MaxStackSize];
		}
		if (suffix == null) {
			suffix = new byte[MaxStackSize];
		}
		if (pixelStack == null) {
			pixelStack = new byte[MaxStackSize + 1];
		}
		// Initialize GIF data stream decoder.
		data_size = read();
		clear = 1 << data_size;
		end_of_information = clear + 1;
		available = clear + 2;
		old_code = NullCode;
		code_size = data_size + 1;
		code_mask = (1 << code_size) - 1;
		for (code = 0; code < clear; code++) {
			prefix[code] = 0;
			suffix[code] = (byte) code;
		}

		// Decode GIF pixel stream.
		datum = bits = count = first = top = pi = bi = 0;
		for (i = 0; i < npix;) {
			if (top == 0) {
				if (bits < code_size) {
					// Load bytes until there are enough bits for a code.
					if (count == 0) {
						// Read a new data block.
						count = readBlock();
						if (count <= 0) {
							break;
						}
						bi = 0;
					}
					datum += (((int) block[bi]) & 0xff) << bits;
					bits += 8;
					bi++;
					count--;
					continue;
				}
				// Get the next code.
				code = datum & code_mask;
				datum >>= code_size;
				bits -= code_size;

				// Interpret the code
				if ((code > available) || (code == end_of_information)) {
					break;
				}
				if (code == clear) {
					// Reset decoder.
					code_size = data_size + 1;
					code_mask = (1 << code_size) - 1;
					available = clear + 2;
					old_code = NullCode;
					continue;
				}
				if (old_code == NullCode) {
					pixelStack[top++] = suffix[code];
					old_code = code;
					first = code;
					continue;
				}
				in_code = code;
				if (code == available) {
					pixelStack[top++] = (byte) first;
					code = old_code;
				}
				while (code > clear) {
					pixelStack[top++] = suffix[code];
					code = prefix[code];
				}
				first = ((int) suffix[code]) & 0xff;
				// Add a new string to the string table,
				if (available >= MaxStackSize) {
					break;
				}
				pixelStack[top++] = (byte) first;
				prefix[available] = (short) old_code;
				suffix[available] = (byte) first;
				available++;
				if (((available & code_mask) == 0)
						&& (available < MaxStackSize)) {
					code_size++;
					code_mask += available;
				}
				old_code = in_code;
			}

			// Pop a pixel off the pixel stack.
			top--;
			pixels[pi++] = pixelStack[top];
			i++;
		}
		for (i = pi; i < npix; i++) {
			pixels[i] = 0; // clear missing pixels
		}
	}

	private boolean err() {
		return status != STATUS_PARSING;
	}

	private int read() {
        if (readBytes >= gifDataLength)
            return 0;
        return gifData[gifDataOffset + readBytes++] & 0xFF;
	}

    private int read(byte[] bytes, int offset, int length) throws IOException {
        if (readBytes >= gifDataLength)
            return -1;
        int toCopy = Math.min(gifDataLength - readBytes, length);
        System.arraycopy(gifData, gifDataOffset + readBytes, bytes, offset, toCopy);
        readBytes += toCopy;
        return toCopy;
    }

    private int read(byte[] bytes) throws IOException {
        return read(bytes, 0, bytes.length);
    }
	
	private int readBlock() {
		blockSize = read();
		int n = 0;
		if (blockSize > 0) {
			try {
				int count = 0;
				while (n < blockSize) {
					count = read(block, n, blockSize - n);
					if (count == -1) {
						break;
					}
					n += count;
				}
			} catch (Exception e) {
				e.printStackTrace();
			}
			if (n < blockSize) {
				status = STATUS_FORMAT_ERROR;
			}
		}
		return n;
	}

	private int[] readColorTable(int ncolors) {
		int nbytes = 3 * ncolors;
		int[] tab = null;
		byte[] c = new byte[nbytes];
		int n = 0;
		try {
			n = read(c);
		} catch (Exception e) {
			e.printStackTrace();
		}
		if (n < nbytes) {
			status = STATUS_FORMAT_ERROR;
		} else {
			tab = new int[256]; // max size to avoid bounds checks
			int i = 0;
			int j = 0;
			while (i < ncolors) {
				int r = ((int) c[j++]) & 0xff;
				int g = ((int) c[j++]) & 0xff;
				int b = ((int) c[j++]) & 0xff;
				tab[i++] = 0xff000000 | (r << 16) | (g << 8) | b;
			}
		}
		return tab;
	}

	private void readGraphicControlExt() {
		read(); // block size
		int packed = read(); // packed fields
		dispose = (packed & 0x1c) >> 2; // disposal method
		if (dispose == 0) {
			dispose = 1; // elect to keep old image if discretionary
		}
		transparency = (packed & 1) != 0;
		delay = readShort() * 10; // delay in milliseconds
		transIndex = read(); // transparent color index
		read(); // block terminator
	}

	private void readHeader() {
		String id = "";
		for (int i = 0; i < 6; i++) {
			id += (char) read();
		}
		if (!id.startsWith("GIF")) {
			status = STATUS_FORMAT_ERROR;
			return;
		}
		readLSD();
		if (gctFlag && !err()) {
			gct = readColorTable(gctSize);
			bgColor = gct[bgIndex];
		}
	}

	private GifFrame readImage() {
		ix = readShort(); // (sub)image position & size
		iy = readShort();
		iw = readShort();
		ih = readShort();
		int packed = read();
		lctFlag = (packed & 0x80) != 0; // 1 - local color table flag
		interlace = (packed & 0x40) != 0; // 2 - interlace flag
		// 3 - sort flag
		// 4-5 - reserved
		lctSize = 2 << (packed & 7); // 6-8 - local color table size
		if (lctFlag) {
			lct = readColorTable(lctSize); // read table
			act = lct; // make local table active
		} else {
			act = gct; // make global table active
			if (bgIndex == transIndex) {
				bgColor = 0;
			}
		}
		if (act == null) {
			status = STATUS_FORMAT_ERROR; // no color table defined
		}
		if (err()) {
			return null;
		}
        decodeImageData(); // decode pixel data
        skip();
        if (err()) {
            return null;
        }
        currentFrame++;
        // create new image to receive frame data
        // createImage(width, height);
        Bitmap image = setPixels(); // transfer pixel data to image
        GifFrame gifFrame = new GifFrame(image, delay);
        // frames.addElement(new GifFrame(image, delay)); // add image to frame
        // list
        resetFrame(gifFrame);
        return gifFrame;
	}

	private void readLSD() {
		// logical screen size
		width = readShort();
		height = readShort();
		// packed fields
		int packed = read();
		gctFlag = (packed & 0x80) != 0; // 1 : global color table flag
		// 2-4 : color resolution
		// 5 : gct sort flag
		gctSize = 2 << (packed & 7); // 6-8 : gct size
		bgIndex = read(); // background color index
		pixelAspect = read(); // pixel aspect ratio
	}

	private void readNetscapeExt() {
		do {
			readBlock();
			if (block[0] == 1) {
				// loop count sub-block
				int b1 = ((int) block[1]) & 0xff;
				int b2 = ((int) block[2]) & 0xff;
				loopCount = (b2 << 8) | b1;
			}
		} while ((blockSize > 0) && !err());
	}

	private int readShort() {
		// read 16-bit value, LSB first
		return read() | (read() << 8);
	}

	private void resetFrame(GifFrame newFrame) {
        // fill in starting image contents based on last image's dispose code
        switch (dispose) {
            case 0:
                // no dispose, leave restore frame as whatever this is
                restoreFrame = newFrame;
                break;
            case 1:
                // use last bitmap pixels
                restoreFrame = newFrame;
                break;
            case 2:
                // fill last image rect area with background color,
                // handle that in setPixels
                restoreFrame = null;
                break;
            case 3:
                // revert canvas to previous, so just leave the original restore frame
                break;
            default:
                // wtf?
                Log.w("Ion", "Unknown gif dispose code: " + lastDispose);
                break;
        }

		lastDispose = dispose;
		lrx = ix;
		lry = iy;
		lrw = iw;
		lrh = ih;
		lastBgColor = bgColor;
		dispose = 0;
		transparency = false;
		delay = 0;
		lct = null;
	}

	/**
	 * Skips variable length blocks up to and including next zero length block.
	 */
	private void skip() {
		do {
			readBlock();
		} while ((blockSize > 0) && !err());
	}
}
